In the roofing industry, a roofing underlayment is typically applied to the deck of a roof prior to application of shingles or other roofing material. The primary goal of the roofing underlayment is to shield the roofing deck from asphalt (from the back surface of shingles) which otherwise would necessitate tearing up the whole deck instead of just the shingles—a costly option—at the time of reroofing. Underlayments can also help to reduce “picture framing” in which the outline of the deck panels caused by irregularities in the deck surface may be visible through the roofing material applied to the roofing deck.
In most cases, the roofing underlayment comprises a felt material composed of cellulose fibers, glass fibers and a mixture thereof that is saturated with a bituminous material such as asphalt, tar or pitch. Roofing underlayments that are saturated with a bituminous material are thick composites (typically 20 to 60 mils thick), which can be hazardous to manufacture due to the presence of a flammable bituminous material. Many of the asphaltic underlayments available in the market tend to wrinkle after being applied to a roofing deck. This is especially the case if the underlayments are rained upon. Other common problems are blowing off due to wind (when shingles are yet to be installed) or the formation of splits lengthwise in the underlayments when they are left exposed for several days.
In addition to bituminous-containing underlayments, the roofing industry has also developed non-bituminous, i.e., non-asphaltic, underlayments. The prior art non-bituminous underlayments typically include TRIFLEX 30 (marketed by Northern Roof Tiles Sales Co. of Ontario, Canada), TITANIUM UDL (marketed by Interwrap, Inc. of Canada), ROOFTOPGUARD II (marketed by Classic Products, Inc and Drexel Metals), KAYE-FLEX UDL (from Kaye Industries, Florida), etc.
Currently, all non-asphaltic underlayments tend to be water-resistant but substantially non-breathable. That is, the non-asphaltic underlayments do not allow air or water vapor to pass through it. As a result, the moisture from the interior of the building is unable to escape to the exterior resulting in damage to the roof over a number of years. Most of the non-asphaltic underlayments also tend to be slippery, especially when wet.
In view of the drawbacks mentioned above with prior art non-asphaltic underlayments, there is a need for providing a non-asphaltic roofing underlayment that is breathable thereby allowing moisture to escape from inside the building, while preventing water and/or moisture from entering the building. In addition, skid-resistance is a highly desirable property of an underlayment to avoid injuries from roofers sliding off of the roof. Also, sealing around nails or other roof penetrations would provide additional protection towards substantially waterproofing the system.